Electric cables



Aug. 2, 1960 H. BURR 2,947,652

ELECTRIC CABLES Original Filed Dec. 18, 1950 3 Sheets-Sheet 1 INVENTOR.H. BUB/P Aug. 2, 1960 H. BURR 2,947,652 ELECTRIC CABLES Original FiledDec. 18, 1950 3 Sheets-Sheet 2 FIG. 3.

IN V EN TOR.

ATTORNEY H. BURR ELECTRIC CABLES Aug. 2, 1960 3 Sheets-Sheet 3 OriginalFiled Dec. 18, 1950 FIG. 6.

FIG. 7.

INVENTOR. H. BU/PE ATTORNEY Ute iateg P ELECTRIC CABLES Harvey Burr,London, England, assignor to International Standard ElectricCorporation, New York, N.Y., a corporation of Delaware Originalapplication Dec. 18, 1950, Ser. No. 201,348,

now Patent No. 2,810,011, dated Oct. 15, 1957. Divided and thisapplication Mar. 8, 1957, Ser. No. 646,188

Claims priority, application Great Britain Dec. 23, 1949 3 Claims. (Cl.154'2.24)

, This invention relates to the manufacture of electric cables and hasparticular reference to multi-conductor telephone cables.

This application is a division of my copending application, Serial No.201,348, filed December 18, 1950, for Electric Cables, now Patent No.2,810,011. a

The basic unit of one form of conventional telephone cable is usuallythe twisted pair of paper insulated conductors. Such twisted pairs areusually made by first applying a helical lapping of paper tape to eachWire and then twisting the insulated wires together. This processinvolves two separate operations and moreover the speed is limited bythe fact that there is a limit to the speed at which the paperinsulation can be applied without breaking. Careful handling isnecessary to avoid stripping off the insulation.

Numerous attempts have been made to avoid applying the paper as ahelical lapping but they have notbeen found completely satisfactory.

It is also known to insulate a pair of wires simultaneously by passingthe wires and an insulating tape through a bath of molten insulatingcompound while the tape is being folded around the wires. This wrappingholds the wires in position as it passes into a cooling bath where theinsulating compound solidifies. This is essentially a very low speedprocess, slower than the conventional method of lapping a tape helicallyaround each wire individually. Moreover the thickness of insulationaround the wires is considerable and the presence of the insulatingcompound renders the wire unsuitable for use in telephone cable.

There is also known a process of applying an insulating strip in theform of an 8 about a pair of conductors leaving air space between eachconductor and surrounding strip. In this type of process the insulatingstrip is necessarily made of stiff insulating material because thematerial retains its S-fold without requiring heat or adhesives to fixthe fold. This type of insulation about a pair of wires isunsatisfactory because the wires are unsupported in the surroundingairspace and the electrical characteristics of the pair Varies to suchanextent along the length of the pair that a cable made up of apiurality of such pairs would be completely unsatisfactory for telephonepurposes. In addition, each pair occupies a greater space than a pair inthe normal type of cable and thus, the construction would lead to anincrease in cable diameter which is costly, as well as, space consuming.

An object of the present invention is to provide means by which twowires forming a pair can be simultaneously insulated to form a compactpair useful in multi-conductor telephone type cable. Another object isto provide such means which enables the two wires to be simultaneouslyinsulated and to be twisted immediately thereafter.

According to a feature of the present invention the two wires to formthe pair are passed through a die through which there is also passed astrip of insulating 2,947,652 Patented Aug. 2, 1960 ice material wideenough to provide at least one turn round each wire, the die being soshaped that the Wires are gradually brought closer together and the saidstrip is rolled around the two wires. The invention will be understoodfrom the following description taken in conjunction with theaccompanying drawings from which it will be appreciated that theinvention comprises an improved process and apparatus for insulatingelectrical conductors particularly for the manufacture of communicationcables.

in the drawings:

Fig. 1 is a purely diagrammatic representation of the apparatus forcarrying out the process according to the invention.

Fig. 2 illustrates diagrammatically a portion of one form of insulatedpair cable according to the invention.

Fig. 3 represents a detail of the apparatus.

Fig. 4 represents in simplified form the insulating die for carrying outthe process.

Fig. 5 represents in perspective a practical form of die.

Fig. 6 shows in greater detail one construction of die.

-Fig. 7 shows in detail another construction of die.

In Fig. 1 conductor wires 1, 2 are supplied from reels not shown andpassed around two pulleys 3, 4 which are braked by means of frictionbelts 5, 6 the tension of which is controlled by weights 7, 8. The twowires then pass through a guide member 9 through which there are twochanneis guiding the wires so that they will approach the insulating die10 at the correct angle. The strip of paper 11 is supplied from a reel,not shown, and passes directly into the guide member 9 which ensuresthat it is fed into the insulating die 10 correctly.

The only function of guide member 9 is to assemble the paper strip andthe wires correctly for feeding into the insulating die. In Fig. 3 thereis shown a cross section of the guide member 9 which will be referred tolater.

Fig. 2 shows on an enlarged scale a portion of an insulated pair ofwires produced by the process. The two wires 1 and 2 are insulated by anS shaped Wrapping of paper 12 of which one side carries distinguishingmarks as shown. It can be seen that the wires are insulated from oneanother and that the inner edges of the insulating paper are held downby the outer turn of paper so that the two wires are completely covered.Returning now to Fig. l. After the two wires and the strip of paper havepassed through the guide member 9 they pass to the insulating die 10which will be described in more detail below. In this die the paper iswrapped round the two wires in the 8 formation shown in Fig. 2. It is tobe mentioned that if desired more turns can be wrapped around the wiresthan the one and a half turns shown in Fig. 2.

The die 10 is heated as is conventionally indicated in Fig. 1, by aBunsen burner 13. As explained earlier this heating facilitates thepassage of the paper through the die. The paper, which is somewhathygroscopic, is passed in an undried condition and therefore containsconsiderable moisture. It is believed that the evaporation of themoisture from the pores of the paper results in the production of avapour cushion which enables the paper to be drawn through a well shapeddie at high speed. In practice the'temperature of the die is fairlyaccurately controlled according to the conditions obtaining by means ofa thermostat, but a temperature of 220 C. represents an average valuewhich has been found satisfactory. The presence of the water vapour alsoproduces an ironing effect so that the coating of insulation is smoothand retains its shape. After the insulated pair emerges from the die 10it passes round the draw ofi capstan 14 which is suitably mounted on asupclear.

port 15 and driven by a motor, not shown. It can be seen that thetension on the wires between the pulleys 3, 4 and the capstan 14 isdetermined by the friction exerted by the belts 5, 6 and can'thereforebe controlled by the correct selection of the weights 7, 8.

This tension is important as it is desirable to apply the insulationwhile the wire is slightly extended so that after the insulated pairleaves the capstan 14 the wires will contract slightly with the resultthat the paper insulation will not be under tension. This provides amargin so that the paper will not be so taut that it is liable to breakif the insulated pair is bent or stretched during the subsequentoperations involved in twisting and laying the insulated pairs upintocable form. After the insulated pair leaves the capstan 14 it passesround a tensioningdevice before being wound onto the take up drum 17.The obiect of the tensioning device is simply to ensure that there isenough tension on the pair to cause the pair to wind correctly on 'thedrum. It is important that the tension on the pair after it leaves thecapstan should be less than that on the pair before it reaches thecapstan as explained above. The form of tensioning device 16 shown issuitable because it does not allow the tension to increase suddenlyowing to any irregularities in the rotation of the take up drum 17.

It is usually desirable to twist the pair before it is laid up into acable both for electrical reasons such as the reduction of cross talkand also to eliminate any tendency for the wires to roll against andunwind the insulation. For this purpose the take up drum 17 is mountedin a twisting yoke 18 which can be rotated about an axis coinciding withthe line of approach of the insulated pair.

This twisting yoke 18 is geared to the drive of the capstan 1 and thegearing can be set to provide the precise twist length required.

Referring to Fig. 3 the guide member 9 consists of two metal blocks 1?,20 provided with grooves 21, 22 through which the wires 1, 2 (seeFig. 1) pass. These grooves 21, 22 which are also indicated in Fig. 1,lead the wires along approaching paths while a strip of paper 11 passesthrough a rectangular channel 23 formed by the shaping of the metalblocks 19 and 26. The channel 23 is in practice only a narrow slitaccommodating a strip of thin insulating paper 11 but it has been shownon a rather exaggerated scale to make the arrangements The slit ishowever appreciably wider than the thickness of the paper to allow forirregularities. The blocks 19, 20 are held together by screws 24, 25.After the wires and paper have passed through the guide member 9 theynext enter the insulating die 10 where the.

process of wrapping the paper longitudinally about the wires takesplace.

Fig. '4 illustrates diagrammatically the principle of the insulatingdie. In Fig. 4(a) there is shown the intake end of the die there beingtwo apertures 26 connected by a narrow slit 27. At the output end of thedie shown in Fig. 4(b) the two aperatures 26 are so close together thatthe slit has virtually vanished. Fig. 4(c) is a plan view of the dieshowing the two channels 26 converging. The diameter of the channels 26is gradually slightly increased as they come closer together since alittle more space is required as the paper is wrapped round the wires.

In Fig. there is shown an exploded view of a prac- The blocks 28 and 29'have arcuate grooves.

30 and 31 have grooves 34 and 35 cut along their appropriate edges. 7 7

It is to be noted that none of the blocks 28, 29, 30, 31 have thegeneral form of rectangular'parallelepipeds. Block 28 is wider at itsdistant end (as shown) than at its near end, and this is also true ofblock 31. Blocks 29 and 39 are wider at their near ends than at theirdistant ends. When these two parts, Figs. 5(a) and (b) are broughttogether the grooves 32 and 33 form with grooves 34 and 35 respectivelythe channels 26 shown in Fig. 4 and the slit 27 is the space betweensurface 36 of block 29 and the under surface 37 of block 30 whichsurfaces it will be seen have been slightly cut away at 38 and 39 fromthe general level of the mating surfaces of the blocks 28, 29 and 3t 31respectively. When the two parts of the die shown in Figs. 5(a) and (b)are brought together the actual die passage will be as shown in Fig. 4and the external shape of the die will be, as drawn, a rectangularparallelepiped. The outer shape of the die is however of no importancein connection with the invention.

There are inevitably some irregularities in the paper and at times itwill be necessary to make a join in the paper as for example when asupply reel is exhausted. It is necessary therefore to arrange theblocks forming the die in such a Way that they can separate slightly toallow a thickened portion of the paper to pass, and such an adjustmenthas to be rather delicate since the paper is fragile.

In Fig. 6 there is shown in more detail a die constructed with thegeneral design described immediately above and illustrated in Fig. 5.

Blocks 28 and 29 are shown mounted on a base plate 40 and rigidly fixedtogether and to the base plate by a screw 41. Blocks 30 and 31 arerigidly fixed together by screw 42, but are slidable on the base plate.A spring 43 acting between a stop member 44 and the top of the unitformed of blocks 30 and 31 keep the unit pressed against the base plate.Another spring 45 acting between a stop member 46 and the side of theunit formed of blocks 30 and 31 keep the unit pressed up against theunit formed of blocks 28 and 29. The stop members 44 and 46 are madeadjustable so that the pressure exerted by the springs can becontrolled.

It can be seen that if a place where the paper strip is thicker or widerthan usual passes into the slit 27 the unit formed of blocks 30 and 31can move upwards or sideways andthepaper will not be damaged. Theentrance to the die may be slightly bell mouthed to enable the oversizepaper to enter and cause the unit to move. The dieneed not however bebuilt up of four blocks and in Fig. 7 there is shown a die formed of anupper block 47 mounted on a lower block 48. The passage through the dieso formed may be of the same shape and proportions as that in the fourblock die of Figs. 5 and 6. It is however still desirable to allow forvariations in the paper width and thickness and this necessitatesdesigning the assembly so that the upper block 47 can move slightly withrespect to the lower block 48 and this involves a somewhat differentstructure from that shown in Fig. 6.

I In Fig.7 the lower block 48 is rigidly fixed to a baseplate 49 whichforms part of a rigid framework 50 by means of screws 51. The upperblock 47 is slidably mounted on the block 48 as shown. It is held inposition by a system of rods which allow it a limitedfreedom ofmovement.

7 Thus rods 52 are. rigidly held in the framework by engagement with thebase plate 49 and the upper member of the frame 50 by the nuts 53.

Where the rods pass through block 47 however they are slightly smallerthan the drillings through which they pass. Thus the upper block is onlypermitted a limited movementin the right and left direction as shown inthe drawing. Similarly one or more rods 54 pass through one or moredrillings in the block 47 which have a diameter slightly larger thanthat of rod 54. The rods are held firmly in position in the framework 50by nuts 55. These rods 54 serve to limit the movement of block 47 in theup and down direction.

The upper block 47 is pressed down onto block 48 by means of spring 56which is compressed between a plate 57 and the upper surface of block47. The pressure can be controlled by means of hand screw 58. Block 47is also pressed to the left as shown in the drawing by means of spring59 which is compressed between plate 60 and the side of block 47.

The pressure can be controlled by the handscrew 61.

It is to be understood that the particular constructions for the die andits assembly illustrated in Figs. 6 and 7 are only examples andproviding the fundamental shape and proportions of the passage throughthe die are maintained any method of mounting the components which isfound suitable may be adopted.

It will be seen that with the process according to this invention wherethe wires issue from the machine they are close together and half thewidth of the paper strip is wrapped around one wire and the other halfaround the other wire, the edges of the strip being on the inside of thetwo lappings so that there is no tendency for the paper to unwrapitself. The paper strip is so wrapped around the wires that one side isexposed around one wire and the other around the other wire, thewrapping is in fact in the shape of a letter S. This has the advantagethat if paper is printed in colour or otherwise marked on one side it isalways possible to identify the wires of a pair.

It has been found advantageous to heat the die when applying paperinsulation as this greatly facilitates the passage and folding of thestrip and also results in the insulation being as it were baked inposition on the wires. A temperature of220 C. has been foundsatisfactory.

It can be seen that this process lends itself to the very rapidproduction of twisted pair as there are no high speed rotating parts. Italso has the advantage that a thinner and/or narrower paper can be usedsince there is less danger of breaking. The insulation on the finishedproduct can be more closely packed than with helical lapping and thismeans that a given number of pairs can be accommodated in a smallercable thus saving some of the expensive sheathing material.

If thought desirable a line of perforations can be provided down themiddle of the original paper strip. These would then appear in themembrane between the insulated wires and would facilitate theirseparation for jointing purposes.

Although the invention has been described in connection with paperinsulation it is not limited thereto. Amongst other applications theremay be mentioned the possibility of using textile tapes, or plasticfihns of rubber strip.

While the principles of the invention have been described above inconnection with specific embodiments, and particular modificationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. Apparatus for insulating two conductors one from the other,comprising an elongated die having an input end and an output end, saiddie having first and second channels of substantially circular crosssection extending longitudinally through the die, said first and secondchannels being parallel to a plane extending through said die, saidfirst channel having its center displaced from one side of said plane,said second channel having its center displaced from the other side ofsaid plane, a third channel of rectangular cross section having itscentral plane lying on said first mentioned plane and having its sidestangential to the lower portion of said first channel and to the upperportion of said second channel at said input end, said first and secondchannels converging front said input end so that continuous portions ofsaid first and second channels tangential with said third channel at itsinput end overlap at said output end of said die, said third channelhaving the cross section of its longitudinal sides decreasing until saidthird channel disappears at the point of overlap of said first andsecond channels, means for traversing a strip of insulating material andsaid two separated conductors through respective channels, and means forheating the die during said traversing.

2. Apparatus as claimed in claim 1, and further comprising means forapplying greater tension to said Wires than to said strip during theirpassage through said die.

3. Apparatus as claimed in claim 1 in which said die is divided into twoseparate portions, and spring pressure holding said two portionstogether.

Barrett Sept. 19, 1893 Barrett Sept. 19, 1893

1. APPARATUS FOR INSULATILNG TWO CONDUCTORS ONE FROM THE OTHER,COMPRISING AN ELONGATED DIE HAVILNG AN INPUT END AND AN OUTPUT END, SAIDDIE HAVING FIRST AND SECOND CHANNELS OF SUBSTANTIALLY CIRCULAR CROSSSECTION EXTENDING LONGITUDINALLY THROUGH THE DIE, SAID FILRST AND SECONDCHANNELS BEING PARALLEL TO A PLANE EXTENDING THROUGH SAID DIE, SAIDFIRST CHANNEL HAVING ITS CENTER DISPLACED FROM ONE SIDE OF SAID PLANE,SAID SECOND CHANNEL HAVING ITS CENTER DISPLACED FROM THE OTHER SIDE OFSAID PLANE, A THIRD CHANNEL OF RECTANGULAR CROSS SECTION HAVING ITSCENTRAL PLANE LYING ON SAID FIRST MENTIONED PLANE AND HAVING ITS SIDETANGENTIAL TO THE LOWER PORTION OF SAID FIRST CHANNEL AND TO THE UPPERPORTION OF SAID SECOND CHANNEL AT SAID INPUT END, SAID FIRST AND SECONDCHANNELS CONVERGING FROM SAID INPUT END SO THAT CONTINUOUS PORTIONS OFSAID FIRST AND SECOND CHANNELS TANGENTIAL WITH SAID THIRD CHANNEL AT ITSINPUT END OVERLAP AT SAID OUTPUT END OF SAID DIE, SAID THIRD CHANNELSTANGENTIAL WITH SAID OF ITS LONGITUDINAL SIDES DECREASING UNTIL SAIDTHIRD CHANNEL DISAPPEARS AT THE POINT OF OVERLAP OF SAID FIRST ANDSECOND CHANNELS, MEANS FOR TRAVERSING A STRIP OF INSULATING MATERIAL ANDSAID TWO SEPARATED CONDUCTORS THROUGH RESPECTIVE CHANNELS, AND MEANS FORHEATING THE DIE DURING SAID TRAVERSING.